<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width,initial-scale=1.0">
    <title>Document</title>
    <style>
        .fade-enter-active,
        .fade-leave-active {
            transition: opacity 0.5s ease;
        }

        .fade-enter-from,
        .fade-leave-to {
            opacity: 0;
        }
    </style>
</head>

<body>
    <div id="app"></div>
</body>
<script src="https://unpkg.com/vue@next"></script>
<script>
    const app = Vue.createApp({
        data() {
            return {
                show: true
            }
        },
        methods: {
            hand() {
                this.anniu = !this.anniu
            }
        },

        template: `
        <div id="demo">
  <button @click="show = !show">
    Toggle
  </button>

  <transition name="fade">
    <p v-if="show">hello</p>
  </transition>
</div>

                `
    })

    const vm = app.mount("#app");
</script>

</html>